Non-smokers who are exposed to secondhand smoke - breathing in environmental smoke from other people's tobacco products - appear to have a higher risk of psychological distress, says a report posted online today that will appear in the August print issue of Archives of General Psychiatry, a JAMA/Archives journal. Secondhand smoke appears also to be associated with a higher risk of future psychiatric hospitalization among healthy adults, the report adds.

As background information in the article, the authors wrote:

A growing body of literature has demonstrated the harmful physical health effects of secondhand smoke exposure. Given the highly prevalent exposure to secondhand smoke - in the United States, an estimated 60 percent of American non-smokers had biological evidence of exposure to secondhand smoke - even a low level of risk may have a major public health impact.

Mark Hamer, Ph.D., of University College London, and team studied 5,560 non-smoking adults (average age 49.8) and 2,595 smokers (average age 44.8) - none of them had any history of mental illness. They had all participated in the Scottish Health Survey in 1998 or 2003. Individuals were assessed with a questionnaire about psychological distress, and admissions to psychiatric hospitals were monitored over 6 years of follow-up. Passive smoking (exposure to secondhand smoke) among non-smokers was assessed using saliva levels of cotinine - the main product formed when nicotine is broken down by the body - "a reliable and valid circulating biochemical marker of nicotine exposure," the authors wrote.

14.5% of the participants reported psychological distress. Non-smokers with a high exposure to secondhand smoke (cotinine levels between 0.70 and 15 micrograms per liter) had a higher risk of psychological distress when compared with those who had no measurable cotinine.

Over the 6-year follow-up, 41 participants were newly admitted to psychiatric hospitals. Smokers and non-smokers with elevated exposure to secondhand smoke were both more likely than non-smokers with low levels of secondhand smoke exposure to be hospitalized for depression, schizophrenia, delirium or other psychiatric conditions.

Previous animal studies have suggested that tobacco may induce a negative mood, and some human studies have also identified a potential link between smoking and depression.

The authors wrote:

Taken together, therefore, our data are consistent with other emerging evidence to suggest a causal role of nicotine exposure in mental health.

(conclusion) To our knowledge, this is the first study to demonstrate a prospective association between objectively assessed secondhand smoke exposure and mental health in a representative sample of a general population.

"Objectively Assessed Secondhand Smoke Exposure and Mental Health in Adults - Cross-sectional and Prospective Evidence From the Scottish Health Survey"
Mark Hamer, PhD; Emmanuel Stamatakis, PhD; G. David Batty, PhD
Arch Gen Psychiatry. 2010;67(8):(doi:10.1001/archgenpsychiatry.2010.76).